Cardioid Microphone – You may have heard of it, but do you know what it does?
This is not the most interesting topic to read about it. However, understanding microphones and the way they operate is crucial. It can help you make decisions in live and recording sessions. Microphone selection and placement are more successful if you have a an understanding of the actions and reactions of the equipment.Frequency response and SPL handling are two characteristics that help determine which microphone you need for a job.
Also keep in mind the different microphone pickup patterns. These refer to the microphone’s direction of sensitivity. They are contained in the structure of the capsule. Microphone placement is determined in regards to not only the instruments being miked, but also other instruments or sounds that are nearby. Understanding these patterns can lead to better placement and more efficient setup time.
The three major pickup patterns are cardioid (unidirectional), bi-directional, and omni-directional. There are other microphone pickup patterns that are variations of the main three. The discussion of those patterns is saved for another day… but probably not. So here are the main three.
The cardioid polar pattern was given its name due to the shape of its pickup pattern, which resembles a heart. It is the most common of the polar patterns.
Cardioid is a unidirectional configuration. Microphones that are unidirectional are most sensitive to sounds coming from a single direction. For the cardioid microphone, this position is at the front of the microphone. The sides and rear reject incoming sound. This is a great tool for reducing feedback on live vocals.
In the recording studio, the cardioid microphone is used for close miking and instrument isolation. It mainly picks up sound from the source at which it is aimed. It rejects sounds at the sides and rear of the microphone.
However, the characteristics that create isolation are also responsible for what is known as the proximity effect. Without getting too involved in the technical explanation, the proximity effect occurs due to phase and pressure differences. As a cardioid microphone is moved closer to a sound source, there is an increase in the sensitivity to bass frequencies. This may be useful in situations where a deeper, low-frequency sound is desired. However, if the sound becomes too boomy, the use of equalization may be required. Always be aware of the proximity effect’s existence. Know how to deal with it.
Have you heard of the little dynamic microphone known as the Shure SM-57? Of course you have! It is the most popular cardioid microphone in the history of the world. Check out some decent budget alternatives.
The second of the three major microphone patterns is the bi-directional configuration. As you can probably determine by its name, the bi-directional pattern is sensitive to frequencies arriving to the capsule from two directions. These two entry points occur at the front of the microphone and at the back of the capsule.
As you can see from the diagram of the bi-directional pattern, it is symmetrical. This is unlike the heart-shaped pattern of a cardioid microphone. Because of this, sounds that are rejected at each side arrive to the front and the back of the microphone capsule simultaneously. The phase difference that creates rear rejection in a cardioid microphone does not exist in bi-directional models. The lack of phase and pressure differences at the two points means no proximity effect for the bi-directional pattern. If placed strategically, a bi-directional microphone may be a great tool for picking up and rejecting multiple sound sources at the same time.
The last of the big three microphone polar patterns is omni-directional. This pickup pattern is characterized by equal frequency sensitivity from all directions. Due to this lack of rejection, an omni-directional microphone is not good for instrument isolation.
However, because it allows sounds to enter from all directions, the omni-directional pattern is often chosen for a room microphone. Adding an ambient microphone to a room can make a recording sound more natural. This offsets the more unnatural qualities of close-miking with a cardioid microphone.
When recording vocals, I use a Radio Shack 33-1070 omni-directional dynamic microphone positioned closely to an Electrovoice unidirectional condenser. This setup creates a more round, warm sound than a cardioid microphone alone. The equal sensitivity of the omni-directional from all directions means not having to deal with the proximity effect. Read more about recording vocals with an omni-directional and cardioid microphone simultaneously.
There are many other microphone pickup patterns. Go check them out if you must.